This invention is generally concerned with apparatus for processing letters and more particularly with thermal printing apparatus for automatically marking stepped or otherwise irregularly-shaped letters including letter mail.
A significant proportion of the approximately one-half billion irregularly-shaped letters, flats, parcels, and other irregularly-shaped mailpieces, such as stepped letter annually received by the U.S. Postal Service for processing, must be manually processed due to the lack of automated equipment. In the case of stepped, and other irregularly-shaped letter mail, automatic separation equipment is available for separating such mail from the main stream of incoming mailpieces, but there has been a long felt need for reliable machinery for handling other processing tasks. In particular, manual processing is heavily relied upon for performing such functions as cancelling the postage of stepped and other irregularly-shaped letter mail, and marking the same with appropriate destination bar codes for subsequent sorting. Moreover, the marking function implemented in the course of processing irregularly-shaped letter mail ranks amongst the highest of the labor intensive activities engaged in by Postal Services on a worldwide basis.
Of course, large private mailers of stepped and other irregularly-shaped letters are similarly burdened with labor intensive processing activities, including applying addresses, postage indicia and bar codes to letters for delivery to the Postal Service.
For marking letters, including letter mail, thermal transfer printing offers an advantage over die cast image transfer processes, in that images transferred by means of thermal transfer printing processes exhibit higher quality image resolution than other printing processes. Although the quality of image resolution is clearly sensitive to irregularities in the shape of the surface area on which the image is printed, such irregularities may be compensated for by subjecting the printhead to high compression loads. On the other hand, continuously subjecting thermal printheads to high compression loads leads to shortening the useful life of the printheads. Nevertheless, for thermal transfer printing on rough-surfaced letter mail, thermal printing structures have been provided wherein the thermal printhead pressure has been held to as low a pressure level as possible without sacrificing the quality of image resolution. In this connection, reference is made to U.S. patent application Ser. No. 000,584 of Danilo P. Buan, Albert C. Chiang and Donald T. Dolan for a Thermal Transfer Printing Apparatus And Method, filed Jan. 6, 1987 and assigned to the assignee of the present invention. On the other hand, thermal printheads have not been adapted for applying a variable pressure for marking stepped or other irregularly-shaped letters, including letter mail.
Accordingly:
An object of the invention is to provide thermal printing apparatus for marking stepped or other irregularly-shaped letters, including letter mail;
Another object to provide thermal printing apparatus including improved means for urging a thermal transfer ribbon and letter into engagement with one another;
Another object is to provide means for resiliently supporting a thermal printhead;
Another object is to provide a flexible roller for use as a platen in thermal printing apparatus;
Another object is to provide a process for controlling thermal transfer printing; and
Yet another object is to provide thermal transfer printing apparatus which includes a flexible roller and resiliently supported thermal printhead which are operatively associated with each other for urging a thermal transfer ribbon and letter into engagement with one another.